Clinical trials of new drugs provide critical data on the drug's effectiveness, dosage requirements and possible adverse side effects. Unlike marketing strategies developed and applied to the introduction and sales of a new drug, it is desired and sometimes necessary in clinical studies to conceal or "blind" the drug to be studied. Blinding the clinical study is believed necessary to prevent bias from the participants--patients, investigators and sponsors--from comprising the results. Blinded studies can also enhance marketability of a product by more credibly demonstrating the favorable health and economic advantages, such as greater therapeutic efficacy and fewer adverse effects, when compared with a marketed drug or placebo. In addition, many governments require blinded clinical studies for approval of a new drug. (See 21 C.F.R. 314.26 and European Union's Directive 91/507/EEC).
Common types of blinding used in clinical studies are outlined in Table 1: